Several RNA viruses are known to be capable of binding a specific amino acid at the 3'-terminus, in a tRNA like manner. The biological function of this property is not known and is the subject of the proposed research. Brome mosaic virus (BMV) is a virus with a divided genome, whose RNA components can be enzymatically charged with tyrosine. It has been shown that the 3' terminal portion of these RNAs are similar to each other in structure and that chemical modification of these segments results in a loss in infectivity. It is also known that charged, but not uncharged, BMV RNA will interact with EF-1-GTP complexes with the resulting hydrolysis of GTP. EF-1 has a similar function of the bacterial elongation factor EF-Tu, which is identical to a subunit of QB replicase. The possibility exists that the aminoacyl-viral-RNA-EF-1 interaction serves as a recognition signal for the assembly of viral replicase subunits at the 3' terminus of the viral genome. We propose to purify the replication complex from virus infected tissue. We will then compare the efficiency of transcription of the viral RNA components in their native state, after aminoacylation and after chemical modification to prevent aminoacylation. Experiments will be carried out to test the in vivo effects of chemically modifying the RNA components. BMV RNA which has had one component selectively modified will be used to infect protoplasts. By comparing the protein and nucleic acid metabolism to infections obtained using unmodified RNAs we will be able to establish the role of the modified area of the RNA in the infection process. BIBLIOGRAPHIC REFERENCES: Bastin, M. and Hall, T.C. 1976. Interaction of elongation factor 1 with brome mosaic virus and tRNAs. J. Virol. 20: 117-122. Kohl, R.J. and Hall, T.C. 1977. Loss of infectivity of brome mosaic virus RNA after chemical modification of the 3' or 5'-terminus. Proc. Nat. Acad. Sci. U.S.A., in press.